This invention relates to a process for the regeneration of glycol solutions loaded with water.
Lower glycols are normally strongly hygroscopic substances, and for this reason mono-, di-, and triethylene glycols have been known for years as desiccants. Thus, these compounds are used, for example, for the drying of gases (U.S. Pat. No. 2,787,451) by introducing the gases at the bottom into a scrubbing tower where they are met by a spray of glycol solution from above. A dried gas is withdrawn from the head of the scrubbing tower in this process. However, glycols are also employed as desiccants for liquids, insofar as these liquids are not miscible with glycol.
Special significance is attributed to the glycols in low-temperature processes where there is the danger of the crystallization of water ice when processing moist liquids or gases, leading to clogging of apparatus parts. In these instances, minor amounts of glycol are added to the gas or to the liquid, before it comes into contact with apparatus parts which are at below 0.degree. C., thereby to prevent a freezing out of water ice.
A typical example for the last-mentioned application is the use in defogging devices (DOS [German Unexamined Laid-Open Application] No. 2,224,671). In these defoggers, utilized for the defogging of airports, freeways, etc., the air is blown by means of a blower over the evaporator and liquefier of a refrigerating machine and, due to the cooling of the air at the evaporator, a condensation or freezing out of the fog is accomplished. Since most of the moisture, in case of outside temperatures of below about +5.degree. C., is precipitated in the form of ice on the evaporator of the refrigerating machine, the heat transfer from the air and/or fog to the evaporator drops rapidly as soon as the ice layer has reached a certain thickness. Therefore, it has been desirable to suppress the deposition of ice on the evaporator at the outset, and for this reason the evaporator is sprinkled, in the conventional process, with an aqueous glycol solution. Since a device as utilized, for example, for airport defogging requires per operating hour about 100-150 kg. of glycol as the antifreeze agent, a regeneration of the glycol must be provided, unless this quantity is to be discarded.
The heretofore customary regenerating method (U.S. Pat. No. 2,787,451) resides in heating the glycol solution and distilling off part of the absorbed water. However, this process has the disadvantage that it requires a large amount of heat energy and cooling water, because large temperature differences must be overcome for the heating and recooling of the solutions. A further disadvantage of the warm regeneration method is that the glycol can be oxidized during heating partially to glycolic acid, which has an extremely corrosive effect on aluminum.